Synonyms

Acipenser rubicundus

Basis for Listing

Once very common throughout the state, overfishing and pollution in Lake of the Woods and the St. Louis River estuary in the Lake Superior drainage nearly extirpated the Lake Sturgeon (Acipenser fulvescens) from Minnesota. The Lake Sturgeon is a long-lived, slow-growing, late-maturing, fish species that does not do well under heavy exploitation. Catch estimates since the early 1890s have declined 99.4%. Siltation, some agricultural practices, and dam construction also reduced habitat availability for the species, resulting in the extirpation or reduction of populations throughout its range. For these reasons, the Lake Sturgeon was listed as a special concern species in Minnesota in 1984 (Hatch et al. in preparation).

Description

The Lake Sturgeon is a primitive fish, with a cartilaginous skeleton. It has 5 rows of large, prominent, bony plates (or scutes) on its body. A small aperture, the spiracle, is present between the eye and the upper corner of the gill cover. The region from the anus to the tail fin is thick and not entirely covered with bony plates. Lake Sturgeon have a flattened snout, with large, fleshy barbels and a protractile mouth located under the head. The lower lip has 2 slightly papillose lobes. The Lake Sturgeon is Minnesota's largest fish and can reach a total length of 2 m (6.6 ft.) and weigh over 45 kg (99 lbs.).

Habitat

Lake Sturgeon prefer moderately clear, large rivers and lakes. They are most often found over firm sand, gravel, or rubble bottoms. The Lake Sturgeon is a migratory species, present in all drainages in Minnesota except the Missouri. It was recently found after a long absence in the Minnesota River, downstream of Granite Falls. Lake Sturgeon are also present in limited numbers in the Mississippi, St. Croix, Red, and Rainy rivers as well as Lake Superior, Lake of the Woods, and some lakes in the Boundary Waters Canoe Area.

Biology / Life History

Found in Minnesota waterways year-round, Lake Sturgeon travel widely in loose aggregations within their range. They require extensive areas of shallow water to find food, lightly dragging their barbels along the bottom in search of prey. Their diet includes insect larvae and other invertebrates, snails, leeches, small mussels, and small fish. Spawning occurs between April and early June, and aggregations can be seen in shallow water (0.3-4.6 m (1-15 ft.)) near shorelines (Becker 1983). Lake Sturgeon are thought to return to natal areas to spawn, and individuals migrate long distances (as far as 201 km (125 mi.)) upstream to spawning grounds. Males arrive at spawning sites before females, often cruising the shallows in groups of eight or more. Spawning begins as soon as a ripe female enters the group, and several males attend one female. Fertilized eggs are adhesive and attach to gravel or rocks until hatching. Females may spawn for 5-8 hours over one or more days. Lake Sturgeon are slow-growing and late-maturing, and they only spawn intermittently. Females spawn once every 4-6 years and typically reach sexual maturity at 24-26 years old, when they are about 140 cm (55 in.) long (Becker 1983). Males spawn every 2-3 years and typically reach sexual maturity at 8-17 years, when they are around 114 cm (45 in.) long. Only 10-20% of adults within a population are sexually active and spawn during a given season (U.S. Fish and Wildlife Service 2008). The largest Lake Sturgeon specimen documented in Minnesota's official angling records was caught in the Kettle River and weighed 42.8 kg (94 lbs. 4 oz.). It measured 178 cm (70 in.) long and 67 cm (26.5 in.) in girth. The largest historical record was from 1903, weighed 181.4 kg (400 lbs.), and measured 457.2 cm (180 in.) long. The maximum life span of Lake Sturgeon is typically 55 years for males and may be more than 150 years for females.

Conservation / Management

Dam construction has restricted the migration of Lake Sturgeon, resulting in limited access to spawning grounds and destruction or degradation of available feeding and spawning grounds. Siltation, pollution, deforestation, and some agricultural practices have also contaminated aquatic habitats, reducing available habitat. Removing barriers to fish passage and re-connecting river habitats offer the greatest opportunity for restoring Lake Sturgeon populations. Efforts to reduce point and non-point pollution should also be encouraged to improve water quality and the condition of spawning grounds. Research needs for the Lake Sturgeon in Minnesota include identification of habitat guilds and spawning areas and further studies into limiting factors and opportunities for fish passage around dams.

Conservation Efforts in Minnesota

The commercial harvest of Lake Sturgeon in Minnesota was closed in the 1930s. Today, sport fishing harvest requires a special tag and is limited to one fish per year from the St. Croix River or Canada-Minnesota border waters (Rainy River and Lake of the Woods). The Minnesota DNR and various partners, including the U.S. Fish and Wildlife Service and local and tribal governments, have been working since 1990 to reintroduce or restore Lake Sturgeon populations in four Minnesota watersheds: Red River, Lake of the Woods/Rainy River, St. Louis River estuary/western Lake Superior, and St. Croix River. Lake Sturgeon are often tagged to allow an estimate of exploitation and to determine population status, movement patterns, habitat components, growth rate, and spawning chronology. Efforts are also being made to determine and protect the genetic identity of Minnesota's Lake Sturgeon populations.

In 2002, the Minnesota DNR began implementing a 20-year stocking plan in the Red River basin, with a goal of re-establishing a sexually mature, naturally reproducing population over the next 20-30 years. About 20,000 fingerlings have been stocked annually into basin lakes and tributaries (Minnesota DNR 2002). Between 1994 and 2012, seven of the eight dams on the main stem of the Red River were modified to allow fish passage. Another 31 barriers on Red River tributaries have been modified or removed, however, 42 structures remain that present significant barriers to fish passage.

The spawning success of the Rainy River Lake Sturgeon population rebounded in the 1970s as a direct result of the federal Clean Water Act (Kallok 2008). Results of a 2004 population study, which also included portions of Lake of the Woods, revealed an expanding population, with consistent recruitment over the last 30 years. Given the large proportion of immature fish, however, this population is still considered to be below recovery goals (Stewig 2005).

The Minnesota DNR stocked 16 Lake Sturgeon year-classes in the St. Louis River estuary between 1983 and 2000. In 2003, the Great Lakes Fishery Commission completed a Lake Sturgeon rehabilitation plan for Lake Superior (Auer 2003). In the spring of 2007, DNR Fisheries staff observed mature sturgeon returning to historical spawning grounds from Lake Superior. Presently, nine Lake Superior tributaries are known to support self-sustaining Lake Sturgeon populations (Auer 2003). In 2009, a cooperative project between The Nature Conservancy, the Environmental Protection Agency, the U.S. Fish and Wildlife Service and the MN DNR restored roughly 245 m (800 ft.) of suitable spawning habitat below the Fond du Lac Dam.

The Minnesota DNR began stocking Big Stone Lake with fingerlings in 2014 (LakeFinder 2016), and commercial fishermen reported catching juveniles in early 2016 (C. Domeier, DNR Fisheries, personal communication). The last time the species was reported in Big Stone Lake was 1940.

The Minnesota DNR conducted a 3-year study of Lake Sturgeon in the Kettle and St. Croix rivers in the mid-1990s, and these populations appear to be stable. In 1995, the Sandstone Dam was removed on the Kettle River, restoring spawning habitat and reconnecting a historically important tributary on the upper river (Kallok 2008).

The Upper Midwest Environmental Sciences Center of the U.S. Geological Survey, in collaboration with the U.S. Fish and Wildlife Service, tagged and conducted radio telemetry studies of 31 Lake Sturgeon in the Upper Mississippi River in 1997 and 1998. Lake Sturgeon in the study exhibited complex movement behaviors and heavily used small, core habitat areas. Dams appeared to pose intermittent barriers to their upstream passage, with an apparent restriction during low to moderate flow conditions. Given the Lake Sturgeon's extensive use of main channel and channel border areas in the Mississippi River, there is a high potential for encounters between sturgeon and commercial barge traffic in the form of propellar strikes, which are usually fatal (Knights et al. 2002). Additional research to determine if this is a limiting factor for recovery of Mississippi River Lake Sturgeon populations may be warranted.

The recent inception of Minnesota’s Clean Water Legacy Program will eventually yield benefits to Lake Sturgeon habitats through nutrient and sediment load reductions.